Many antimetabolites such as 5-fluorouracil and 5-azacytidine are believed to exert their antitumor effects, at least in part, by being incorporated into messenger RNA and initiating miscoding during translation. To test this hypothesis, poly(A)- containing RNA from polysomes of regenerating rat liver is being isolated and analyzed in an in vitro protein synthesizing system prepared from wheat germ. The labelled translation products are being analyzed by SDS-polyacrylamide gel electrophoresis, isoelectric focusing in polyacrylamide gels and scintillation autography (fluorography). In adddition, poly(A)RNA will be analyzed for chemical modification of its 3'- and 5'-termini as well as rate of synthesis and alteration of size distribution resulting from treatment with the anticancer drugs.